Sapphire is a single crystal aluminum oxide and has a Mohs hardness only lower than diamond. Due to the special mechanical, thermal, electrical properties as well as good radio-resistance, heat conduction, and stable chemical characteristics of sapphire, sapphire is widely used in the defense industry, aerospace research and civilian area. Conventional mechanical methods for sapphire cutting such as diamond wire-sawing typically suffer from low machining speed, machining freedom, processing quality, and accuracy. In addition, such contact-type cutting tools using diamond wires do not last long and have a high level of wastage. In contrast, laser cutting technology has high-energy density, and contactless features, the restrictions on the cutting requirements caused by the contact stress of machining tools are thus effectively avoided. However, for hard, brittle materials such as sapphire, laser cutting technology based on thermal ablation still cannot solve problems such as cracking, slagging, and collapsing, which adversely affect cutting depth, cutting width, surface roughness, select of cutting free path and cutting efficiency. As the advancement of sapphire application tends towards to a direction which requires thinner sapphire with higher surface quality and better damage resistance, it imposes an urgent and extremely difficult challenge to the fine cutting technique of sapphire. Technology breakthroughs are achieved in the cutting depth, kerf taper and cutting surface quality.
Chinese patent CN201510239300.X disclosed a method for obtaining crack direction and offset in sapphire laser cutting and adjusting laser machining position according to the crack direction and offset to finish the remaining cutting path. However, the cutting mechanism of this patent is still based on laser thermal ablation, in which sapphire chips with front and back electrodes are processed, and machining accuracy of cutting surface is not involved. Chinese patent CN201410204028.7 disclosed a compound sapphire processing method which involves processes of nanosecond laser heat treatment, ultrasonic chemical corrosion pretreatment, picosecond laser precision machining and post-ultrasonic abrasive polishing. These four processes are sequentially performed and are not performed simultaneously; Operation time of the four processes is long and tedious. Chinese patent CN201210290741.9 used picosecond (10−12 s) and femtosecond (10−15 s) laser. By focusing the laser beam on the surface of a transparent material and forming a waveguide structure with the incident beam, waveguide planar is formed by controlling the laser moving at a constant speed along the direction which perpendicular to the material surface. Waveguide area relates to refractive index change area of the material. and there is no material disruptive failure. However since different transparent materials are associated with different material systems and different crystal systems and structures, the practicability of using waveguide region to form material fracture surface is not generalizable. An embodiment of the patent is glass, and glass is amorphous. However, the sapphire used in the present application is much harder than glass. Chinese patent CN201410657880.X used 30-55 W picosecond laser to process sapphire surface by means of galvanometer scanning. It belongs to laser marking technology on the sapphire surface and does not involve cutting depth and precision. Chinese patent 201410379877.6, 201410380104.X and 201410380147.8 disclosed methods and apparatus for forming filaments in transparent materials using a laser. By generating multiple focal points by a distribution—type focus lens module such that the main focal point doesn't reside on the material being processed, holes with specific depth and width are generated through filamentation. German scientists Maren Hörstmann-Jungmann et al. disclosed forming microchannels on the sapphire surface or within sapphire by utilizing the nonlinear effect of a tight focused femtosecond laser, then generating hollow microstructures by chemical ultrasound (J. Laser Micro Nanoengineering, 2010, 5(2): 145-149). The depth of laser machining using this method is limited by laser focal depth. Also, the way of tight focusing femtosecond laser has to be followed by ultrasonic chemical processing. This method overcomes the limitation of machining depth by compensating power and improving the focus, while at the same time, by utilizing the catalytic effect of microthermal heating of picosecond laser irradiation on chemical corrosion was studied by using, the isolation of the sapphire sample along the processing path is obtained.